feat(jobs): emit job.enqueue + worktree.pruned audit rows

Deferred audit retrofits from Plan #5 self-review:
- WebhookNotifier now records a job.enqueue audit row after each
  successful repo.Enqueue (best-effort: failures are warn-logged, not
  propagated). Added optional audit.Recorder + *slog.Logger params to
  NewWebhookNotifier.
- WorktreePrune.executionPhase now records a worktree.pruned audit row
  after each successful FinishPruneSuccess. Added optional audit.Recorder
  param to NewWorktreePrune.
- app.go wires the existing auditRec into both constructors.
- integration_test.go: drop the _ = auditRec suppression and pass
  auditRec into the webhook notifier so the closed-loop test exercises
  the audit emit path.

internal/app/app.go

@@ -254,7 +254,7 @@ func New(ctx context.Context, cfg *config.Config, dist embed.FS) (*App, error) {
 		Enabled: cfg.Notify.Webhook.Enabled,
 		Topics:  cfg.Notify.Webhook.Topics,
 		Backoff: webhookBackoff,
-	}, clock.Real())
+	}, clock.Real(), auditRec, log)
 	notifyDispatcher.Register(webhookNotifier)
 
 	dispAdapter := dispatcherAdapter{d: notifyDispatcher}
@@ -269,7 +269,7 @@ func New(ctx context.Context, cfg *config.Config, dist embed.FS) (*App, error) {
 		runners.WorktreePruneConfig{
 			IdleThreshold: cfg.Jobs.WorktreePrune.IdleThreshold,
 			WarningLead:   cfg.Jobs.WorktreePrune.WarningLead,
-		}, log)
+		}, log, auditRec)
 	attCleanupRunner := runners.NewAttachmentCleanup(
 		chatAttachmentAdapter{repo: chatRepo},
 		attachStorage,